Abstract P006: Targeting the zymogen granule protein 16B (ZG16B) to suppress breast cell growth and invasiveness

Abstract

Abstract The induction of tumor suppressing effects by retinoid X receptor-selective agonists in premalignant breast cells may become ineffective in the course of malignant transformation. Therefore, this study aimed to identify pro-tumorigenic factors suppressed in a rexinoid-dependent manner, hypothesizing that such a mechanism may remain active and relevant for cancer interception throughout the various stages of breast cell transformation. To minimize toxicity due to long-term rexinoid treatment in the prevention setting, an additional goal was to identify synergistic growth suppressive combinations of bexarotene (Bex) in normal mammary epithelial cells. The selected combination of Bex and a non-selective beta-adrenergic inhibitor carvedilol (Carv) from an unbiased high throughput screen demonstrated marked cancer preventive activity in a mouse model of Her2-induced ER-negative breast cancer at subtherapeutic doses. To elucidate the molecular underpinnings of this chemopreventive activity, genes selectively suppressed by the drug combination over the individual agents were sought. We determined that the zymogen granule protein 16B (ZG16B), a secreted prognostic marker in breast cancer, was suppressed in normal breast cells by the combination of Bex and Carv. Chromatin immunoprecipitation following Bex+Carv treatment revealed enrichment of the chromatin remodeler protein ARID1A at sites of decreased H3K27 acetylation within the enhancer of the ZG16B gene, resulting in a marked down-regulation of ZG16B. Cell-free supernatant containing overexpressed recombinant ZG16B triggered Erk phosphorylation, increased the proliferation and migration of immortalized HME-hTert cells and induced the expression of extracellular matrix proteins. Furthermore, ZG16B promoted mesenchymal characteristics similar to TGF-b, which was inhibited by an antibody against ZG16B. When administered in tandem, ZG16B neutralized the effects of Bex+Carv. In breast cancer cells, ZG16B stimulated the migration of all tested cell lines, but enhanced proliferation only in ER-positive MCF-7 and T47D cells. Anchorage independent 3D growth of both ER-positive T47D and ER-negative MDA-MB231 cells was stimulated by ZG16B, while Bex+Carv reduced colony formation and suppressed ZG16B levels. Taken together, ZG16B is a potent factor in the growth, mesenchymal transition and invasiveness of breast epithelial cells at all stages of transformation. Our data further suggest that ZG16B may represent a relevant target of the tumor suppressing activity of rexinoids and the combination of Bex+Carv. Citation Format: Máté Lengyel, Iván P. Uray. Targeting the zymogen granule protein 16B (ZG16B) to suppress breast cell growth and invasiveness. [abstract]. In: Proceedings of the AACR Special Conference: Precision Prevention, Early Detection, and Interception of Cancer; 2022 Nov 17-19; Austin, TX. Philadelphia (PA): AACR; Can Prev Res 2023;16(1 Suppl): Abstract nr P006.